Hi Didac,
Appreciate for your insightful reply!! I will try to use bondwire for testing first. Actually my design is only 2.4GHz VCO with some modulation. But the receiver can be very close to the antenna. I saw a paper for similar application just use the big on-chip inductor for transmitting RF signal. Their carrier frequency is even lower, around 500MHz.
By the way, what kind of bondwire material you think it's better? Gold or Aluminum? How about thickness? how to control the antenna impedance roughly? Thank you very much! My chip will be embedded into rodent's head, so I want to make it as small and light as possible.
Le
didac wrote on Sep 5th, 2007, 7:05am:Hi sapphire,
Assuming that you are at a high frequency(λ/4 at 15GHz are 5 mm which is a long bondwire) and you are using your IC as chip on-board without any epoxy above, I think that several aspects will limit the performance of this kind of antenna:
1)This antenna is by definition a monopole,not a dipole, you are taking the feeding point at the contact point not in a balanced manner in the middle of the antenna. The monopole need a ground plane under it and what you will have is the IC and probably the first layer of dielectric material of the PCB(unless you put a ground plane just under the chip that can complicate the PCB design).
2)Adjacent bondwires can modify the impedance of the antenna due to the proximity, this is important to take into account.
3)From a electromagnetic point of view I don't know in which angle the bondwire will be floating, a monopole has a radition null along it's axis, also I don't know if the bonding pad will suffer from mechanical stress. Another possibility is that the floating bondwire could move and short-circuit to adjacent bondwires.
The most common integrated antennas I've seen are from the printed family(using microstrip), try a fetch at IEEE and take a look
Hope it helps,